Zeolites photooxygenation

Scheme 21 Hydrogen bonding effects 3.1.9 Photooxygenation in Zeolites...

Fig. 15 Comparison of product mode (ene versus [2 + 2] and [4 + 2]) in Wagnerova Type I photooxygenations in solution and in the interior of a zeolite.

The majority of intrazeolite photooxygenations have been conducted in NaY,84 85 however, one study in the pentasil zeolite ZSM-5 demonstrates that steric confinement effects can play important roles.84 A comparison of the reactions of a series of tri-substituted alkenes in isooctane, NaY, and in ZSM-5 is given in Fig. 21. The reactions... 

Fig. 22 Effect of zeolite enforced physical separation of substrate and sensitizer on product distribution in photooxygenation of 1,4-diphenyl-1,3-butadiene.

The Frei photooxygenations in Fig. 32 were all conducted by irradiation of the zeolite powder in the absence of solvent. Solvents shield the substrate from the electrostatic field of the cation and reduces the magnitude of the bathochromic shift.122 Kojima and coworkers reported that irradiation of traw.v-stilbenetajNaY in... 

In order to rationalize the complex reaction mixtures in these slurry reactions the authors suggested that irradiations of the oxygen CT complexes resulted in simultaneous formation of an epoxide and dioxetane36 (Fig. 34). The epoxide products were isolated only when pyridine was co-included in the zeolite during the reaction. Collapse of the 1,1-diarylethylene radical cation superoxide ion pair provides a reasonable explanation for the formation of the dioxetane, however, epoxide formation is more difficult to rationalize. However, we do point out that photochemical formation of oxygen atoms has previously been observed in other systems.141 All the other products were formed either thermally or photochemically from these two primary photoproducts (Fig. 34). The thermal (acid catalyzed) formation of 1,1-diphenylacetaldehyde from the epoxide during photooxygenation of 30 (Fig. 34) was independently verified by addition of an authentic sample of the epoxide to NaY. The formation of diphenylmethane in the reaction of 30 but not 31 is also consistent with the well-established facile (at 254 nm but not 366 or 420 nm) Norrish Type I... 

Stratakis, M. (2003). Selective photooxygenation of alkenes by zeolite confinement. In 13th European Symposium on Organic Chemistry, Medimond, V. (ed.), pp. 15-20. Medimond Publishing Co., Bologna... 

Blatter, F., Moreau, F. and Frei, H. (1994). Diffuse reflectance spectroscopy of visible alkene-02 charge transfer absorptions in zeolite Y and determination of photooxygenation quantum efficiencies. J. Phys. Chem, 98(50), 13403-13407... 

Kojima, M., Nakajoh, M., Matsubara, C. and Hashimoto, S. (2002). Photooxygenation of aromatic alkenes in zeolite nanocavities. J. Chem, Soc. Perkin Trans. 2, 1894-1901... 

Takeya, H., Kuriyama, Y. and Kojima, M. (1998). Photooxygenation of stilbenes in zeolite by excitation of their contact charge transfer complexes with oxygen. Tetrahedron Lett. 39, 5967-5970... 

ZSM-5, 228, 229, 246, 247-248 Zeolites, oxygenations in Wagnerova Class I intrazeolite photooxygenation, 233-253... 

For the achievement of mass balances in intrazeolite photooxygenation reaction, >80%, loading levels of 0.1-0.3 adsorbed molecules per zeolite supercage have been successfully used in the past. However, the recent observation by Pace and Clennan, that replacing the solvent hexane with peril uorohexane was very crucial for the efficiency of the reaction, allowed the zeolite medium to be used for preparative scale photooxygenation reactions (500 mg of alkene), without loss of the product selectivity or the reduction of the mass balance. 

Due to the confined environment and cation-jr interactions within the zeolite cavities as well, it is expected that the regioselectivity in the photooxygenation of trisubstituted... 

TABLE 22. Photooxygenation of isobutenylarenes 20 and 137-146 within the thionin-supported zeolite Na-Y... 

It has already been mentioned (Section III) that the study of the diastereoselection in the electrophilic addition of singlet oxygen to the n face of chiral alkenes is of primary interest for the achievement of a selective oxyfunctionalization reaction. Zeolite confinement and cation- 7r interactions might be expected to affect significantly the diastereoselectivity in the photooxygenation of chiral alkenes. 

Michael Orfanopoulos, Georgios C. Vougioukalakis and Manolis Stratakis TABLE 25. Photooxygenation of (R)-(—)-Q -phellandrene in zeolite and in solution... 

SOD see Superoxide dismutase Sodium, zeolite Na-Y photooxygenation, 870-4, 885-6, 887 Sodium borohydride, hydroperoxide determination, 687, 690, 691, 692 Sodium hypochlorite, aUyhc hydroperoxides, 673... 

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